Late Paleozoic rare-metal granitoid magmatism of the Southern Baikal region

The Late Paleozoic intraplate magmatism of the Selenga-Vitim structural zone of the Baikal region (Khamar-Daban Range) produced granitoids of different geochemical types: palingenic calc-alkaline granitoids, subalkaline monzogranites, and rare-metal Li-F granitoids and their subvolcanic analogues. Subalkaline and rare-metal granitoids occur in the periphery of the Late Paleozoic magmatic zone. Rare metal granite magmatism is manifested in this region as nearly N-S trending intrusive-dike belts comprising multiphase intrusions (Kharagul, Urugudei, and Bitu-Dzhida massifs) with an exposed area of ∼10 km² and an age of formation from 311 to 321 Ma and series of accompanying dikes. The early phases of the intrusions are made up of biotite granites usually with fluorite, which are changed during the late stage by typical topazbearing rare-metal amazonite-albite granites. In the subvolcanic facies, thicker subalkaline dikes of monzonite porphyry, granite porphyry, and elvan are changed by ongonites, topaz rhyolites, and topazites, which occasionally serve as cement in eruptive and fluid-explosive breccias. The development of multiphase intrusions from early biotite granites to late amazonite-albite granites with Li-F mica was accompanied by an increase in SiO₂ and, especially, Na₂O contents, whereas the level of (FeO + Fe₂O₃), CaO, and K₂O declined. Geochemical evolution includes an increase in the same direction in the contents of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease in Ba, Sr, Zn, Zr, Th, and U. Similar evolution is also characteristic of the subvolcanic rocks, which emphasizes the genetic relation of the whole intrusive-dike complex of the Khamar-Daban province. Significant differences were detected in the distribution of K, Ba, Sr, and Zr between the calc-alkaline granitoids and rare-metal Li-F granites. The continental crust-normalized patterns of the raremetal granites show positive anomalies for Li, Rb, Nb, and Pb. The rare-metal Li-F granites could not be produced by palingenesis only, and their formation required specific conditions causing extensive accumulation of characteristic trace elements. During the evolution of granite melts, Li, Rb, Ta, Nb, Sn, W, and F are extensively accumulated in late intrusive phases, which indicates an important role of the processes of magmatic and fluid-magmatic differentiation during their formation. The composition and isotope geochemical characteristics of the supposed magma source material correspond to the ancient Precambrian continental crust with a mean model age of more than 1200 Ma.     

藏南拿日雍措片麻岩穹窿淡色花岗岩稀有金属的富集

拿日雍措穹窿(错那洞穹窿)位于北喜马拉雅穹窿的东部,穹隆内花岗岩种类较多,有淡色花岗岩、含石榴子石淡色花岗岩、片理化淡色花岗岩、含石榴子石和含绿柱石伟晶岩.这些花岗岩为经历了斜长石、锆石、独居石、磷灰石、富Ti矿物等分离结晶作用而形成的高度演化花岗岩,相对于维氏世界花岗岩平均值,富集Bi、Cs、Li、Sn、Be、Pb、B、W、Ta等稀有金属成矿元素,略贫Nb元素.同时,围岩也相对富集稀有金属元素.全岩地球化学分析表明,引起拿日雍措穹隆淡色花岗岩富集稀有金属成矿元素的因素是分离结晶作用和热液交代作用.高度演化淡色花岗岩在喜马拉雅造山带广泛分布,铌铁矿、钽铁矿、锡石和绿柱石等稀有金属矿物已在多处露头被识别,暗示了喜马拉雅淡色花岗岩是未来稀有金属矿产勘探的重要靶区.     

Geochemistry, geochronology and mineralisation potential of the granites in the Central Iberian Zone: The Jalama batholith

The Jalama batholith (Spain and Portugal) is one of the numerous granites of the Central Iberian Zone with Sn- and W-associated mineralisation. On the basis of petrographical and geochemical characterisation three types of granite have been distinguished: inhomogeneous granitoids, porphyrytic granites and leucogranites, all of these being peraluminous and subalkaline. All the granites correspond to S-type granites. The field data, the petrography and lack of geochemical affinity relationships of the leucogranites with the remaining granites indicate that their geneses correspond to an independent magma batch and superimposed fractional crystallisation process. The granitic units show subparallel REE patterns. There is a decrease in total REE and an increase in the negative Eu anomaly from the inhomogeneous granitoids to leucogranites. Some leucogranites show relatively low contents of Sn and W almost certainly due to segregation in the magma of a melt rich in water carrying Sn-W. These elements are concentrated in the water phase, which eventually gives rise to Sn-W-associated mineralisation.The ages obtained by means of a whole-rock Rb-Sr isochron for the granites mainly indicate an early intrusion of the inhomogeneous granitoids (319±10 Ma), followed in time by porphyrytic granites (279±9 Ma), which can be associated to the late-post-kinematic granites within the third Variscan deformation phase (D₃).Apart from the average Sn content, the variations of trace elements, principally Sr, Ba, Rb, Th and P, establish that the porphyritic granites and the inhomogeneous granitoids will be barren granites while the leucogranites and the subfacies at the margin of the porphyritic granites correspond to granites with mineralisation potential. It is precisely in these granites of the Jálama batholith that the Sn-W mineralisation is located, for which the criteria utilised has been demonstrated to be effective.     

南岭地区成钨、成锡花岗岩组合的几个判别标志

南岭地区钨锡多金属成矿作用和区内中酸性-酸性花岗岩有着密切的成因联系。利用已发表的和野外收集的地质资料,本文尝试对区内成钨锡花岗岩组合(包括与钨锡矿相关的含钨锡花岗岩和成钨锡花岗岩)进行宏观地质判别。判别过程采用循序渐进的方式,首先将成钨锡花岗岩组合与不成矿花岗岩相区别,然后将含锡花岗岩和含钨花岗岩互相区别开来。相对于不成矿花岗岩,成钨锡花岗岩组合通常具有W、Sn、F、B化探组合异常、多期多阶段演化特点、适度的构造叠加(即存在明显的热液活动)等共同特点,且三者缺一不可。不成矿花岗岩一般具有W、Sn、F、B化探组合为背景值,岩性单一,少见晚期岩株、岩脉(演化不充分)及蚀变的特征。在野外地质工作中,含锡花岗岩一般为花岗闪长岩-二长花岗岩-二云母花岗岩岩性组合。基性端元以普遍发育暗色微粒包体、常见角闪石、含较多的黑云母为鉴别特征。酸性端元中可以含有少量白云母。而含钨花岗岩以黑云母二长花岗岩-二云母花岗岩-白云母花岗岩岩性组合为主,常见含B矿物电气石,基性端元少见或不见角闪石、含较少的黑云母,仅见变质岩、围岩捕掳体和黑云母团块,酸性端元白云母含量较高等组合特征可以与含锡花岗岩相区别。     

Rare-metal mineralization in granitic rocks of the Tongolo Anorogenic Complex — Northern Nigeria

The Tongolo Anorogenic Complex consists of peraluminous biotite granites and peralkaline riebeckite granites in which mineralization is spatially associated with the peraluminous biotite granites. Metallization is dominated by Nb-Sn and Sn-W types. Geochemical analyses of fresh bedrock samples indicate that the Tongolo biotite granites are characterized by enhanced values of a suite of trace elements (Sn, Nb, W, Zn, Rb, Li, F, Th, Y, U) which readily identify them as “specialized” granites. These geochemical data are also examined by R-mode factor analysis with the primary objective of isolating the significant factors accounting for the sample composition as derived from mineralization, alteration and lithology. The resulting orthogonal varimax solution yields a three-factor model that accounts for 79.7% of the total variance. These granite series are marked by what is interpreted as the “lithophile factor” (heavily loaded by Li, Rb, F, Th, Ga, Y, U) dominated by magmatic processes and metallization factors (Nb, Zr, Ga, U, Zn, Li and Sn, W, Rb, F, Th) which are dominated by postmagmatic processes. The two dominant types of mineralization (Nb-Sn and Sn-W), although characterized by the same pattern of trace-element enrichments, can be discriminated on the basis of Rb/Zr and Sn-Li-F relationships.     

南岭稀土花岗岩、钨锡花岗岩及其成矿作用的对比

南岭地区的钨锡和稀土矿床都与花岗岩类有直接成因联系,但二者的成矿作用有许多不同之处.钨锡是典型的热液成矿,而稀土则主要形成于风化作用.随着花岗岩类的分异演化,岩石中的W、Sn等元素含量逐渐增加,因此钨锡等矿床主要与高度分异演化的晚阶段小岩体有关;但是稀土的表现与钨锡不同,由于花岗岩类的分异演化导致稀土栽体黑云母及许多副矿物的减少,因此稀土元素含量在晚阶段岩体中反而降低.赣南的五里亭-大吉山岩体、桂东北的花山-姑婆山岩体等提供了很好的范例.因此,南岭地区与风化壳型稀土矿床有关的岩石主要有:印支期准铝质花岗岩,燕山期A型花岗岩,燕山中-晚期黑云母二长花岗岩等.     

An Inductively Coupled Plasma Spectrometric Method for the Determination of Six Indicator Elements for Mineralization Processes in Granites

A simultaneous multi-element method is described for the determination of six elements of importance in geochemical investigations of mineralization processes in granites. After a mixed acid sample digestion, the elements Be, Li, Nb, W, Mo and Sn are determined by inductively coupled plasma spectrometry. Possible sources of bias due to incomplete sample dissolution and from spectral interferences were investigated. Analysis of 16 geological reference standard samples and a number of enriched samples demonstrates the accuracy and precision of the method for the study of mineralized granites and for several other geochemical sample types as well.     

江西云山复式岩体的地球化学特征及与锡成矿关系探讨

江西永修县云山岩体位于九岭隆起北侧,为二云母花岗岩复式岩体,其地球化学特征表明它是一种富硅、富碱、贫钙、过铝且富轻稀土的陆壳重熔型花岗岩,岩浆分异程度较高。云山岩体中Sn、W含量较高,为锡矿床提供了丰富的成矿物质来源,岩浆侵入与构造活动为成矿作用创造了条件。岩浆在侵位过程中进行了较为彻底的结晶分异,最终成矿物质在云山复式岩体呈岩舌、岩瘤状突出转折部位内接触带构造及各次级构造中富集成矿。在总结区内找矿标志的基础上,根据区内地、矿、物、化、遥等找矿信息,共圈定邓家山-桐木坑、余白田-红花脑、周田-王家岭、大杨-刘家坪、庵塘-马颈、板家塘-板家坳、耕源、佛祖山-焦冲等预测区8处,具有一定找矿潜力。     

Metallogeny and Mineralization Potential of the Bazman Granitoids,SE Iran

The Mesozoic Bazman granitoids are located in Sistan and Baluchestan province, southeastern Iran. Geology of the study area consists of Carboniferous shale, sandstone, and limestone and Permian siltstone, shale, sandstone, limestone, and dolomite that were intruded by the Bazman granitoids. These granitoids include various phases of granite, granodiorite, quartz‐monzodiorite, monzodiorite, diorite, and gabbro. They are metaluminous to slightly peraluminous, reduced, calc‐alkaline and I‐type, and display geochemical characteristics of continental margin (ensialic) granitoids. In this paper, field, petrography, and geochemical data were used to discriminate the Bazman granitoids either as productive or barren granitoids. Although there are a few skarn‐related mineral occurrences adjacent to the Bazman granitoids, most exposed intrusions are not hydrothermally altered and mineralized. Rb/Sr, Zr/Hf, and K/Rb ratios indicate that the granitic magmas that formed most of the Bazman granitoids indicate that they are moderately evolved and have generally not undergone post‐magmatic hydrothermal activity. The Sm/Eu and Rb/Ba ratios and the concentrations of Rb, Ba, and Sr within the aforementioned granitoids show that the rocks are similar to the averages of granitoids devoid of Li, Be, U, Sn, W, and Ta deposits. The I‐type arc characteristics and other geochemical features of the Bazman granitoids show that they are not typical of parental magmas to Sn, W, Mo, and Zn mineralization, but are mainly fertile for Cu and Fe (Au) skarn‐related granitoids.     

湖南锡田矿田花岗岩时空分布与钨锡成矿关系:来自锆石U-Pb年代学与岩石地球化学的约束

锡田钨锡多金属矿田位于南岭成矿带中段,发育多期次岩浆活动与钨锡成矿. 为了厘清花岗岩与钨锡成矿的时空关系,采用野外调查、显微鉴定、锆石U-Pb同位素定年与岩石地球化学的方法对矿田内多期次花岗岩岩体（脉）的空间分布、岩石类型、成岩时代、地球化学组成等进行了研究. 结果表明,锡田矿田发生了三期岩浆事件,分别为加里东期（435~441 Ma）、印支期（220~230 Ma）、燕山期（141~160 Ma）;三期花岗岩普遍富集大离子亲石元素Rb、K、U、Th等,亏损Ti、P、Sr、Ba等微量元素,具明显的负Eu异常,其中加里东期花岗岩与印支期花岗岩为S型花岗岩,而燕山期花岗岩为A型花岗岩;不同时期花岗岩中的成矿元素从加里东期→印支期→燕山期逐渐升高,特别是W、Sn元素在燕山期白云母与二云母花岗岩中最为富集,这与华南地区燕山期钨锡大爆发的时间是一致的;印支期岩体接触带发育少量矽卡岩型Fe-Cu-W多金属矿床,燕山期岩体接触带也发育矽卡岩型W-Sn多金属矿床,并在附近陡倾的张裂隙中发育多个中大型石英脉型W-Sn矿床,而加里东期岩体附近尚未发现钨锡矿化. 因此,锡田矿田的多期次花岗岩与钨锡多金属成矿是时空耦合的,且成矿以燕山期矽卡岩型与石英脉型钨锡矿为主.      

Abdar-Khoshutula intrusive-dike series: Evolution and origin of granitoids in Early Mesozoic magmatic area (Central Mongolia)

The dike belt and separate intrusive bodies of the Abdar–Khoshutula series were formed in the NE-trending linear zone, southwest of the Daurian–Khentei batholith, in the peripheral part of the Early Mesozoic magmatic area, on the western termination of the Mongol–Okhotsk belt. The granitoids of this series are subdivided into following geochemical types: anatectic granitoids of the calc-alkaline and subalkaline series, alkaline rocks, and plumasite rare-metal leucogranites (Li–F granites). The entire series was formed within approximately 12–15 Ma. Its geochemical evolution follows two trends, which correspond to two stages of the granitoid magmatism. The early stage was responsible for the formation of granitoids of two phases of the Khoshutulinsky Pluton and alkaline syenites with similar trace element distribution patterns. However, syenites, as agpaitic rocks, are significantly enriched in Ba, Zr, and Hf. The late stage of the intrusive- dike series resulted in the formation of the dike belt and Abdar Massif of rare-metal granites. These rocks show enrichment in Li, Rb, Cs, Nb, Ta, Sn, and Y, and deep negative anomalies of Ba, Sr, La, and Ce, which are best expressed in the late amazonite–albite granites of the Abdar intrusion and ongonites of the dike belt. The intrusive-dike series in the magmatic areas of different age of Mongolia and Baikal region are characterized by the wide compositional variations, serve as important indicators of mantle-crustal interaction and differentiation of granitoid magmas, and could highlight the nature of zonal areas within the Central Asian Fold Belt. Obtained geochemical data indicate a potential opportunity to concentrate trace and ore components during long-term evolution of the intrusive-subvolcanic complexes, which could be indicators of the evolution of the ore-magmatic systems bearing rare-metal mineralization.     

南岭地区钨锡花岗岩的成矿矿物学：概念与实例

南岭地区的钨锡成矿作用与花岗岩岩浆活动有十分密切的关系。花岗岩的物源与成矿元素的初始富集、花岗岩的分异程度和花岗岩中流体性质与活动性集中体现了花岗岩对成矿的控制能力,即花岗岩的成矿能力。初步建立了南岭地区钨锡花岗岩的成矿矿物学研究体系。黑云母、榍石、锆石、锡石、金红石、黑钨矿、白钨矿和钨铁铌矿等是讨论的重点矿物,它们可用于判别花岗岩的成矿能力。首先以矿物晶体化学为基础,介绍了上述矿物在钨锡花岗岩中的岩相学特征、内部构造和矿物化学及其变化,并分别论证了花岗岩原始含矿性、花岗岩结晶演化和花岗岩中成矿元素活动性的矿物学标志;其次,系统对比了南岭地区三类钨锡花岗岩（准铝质含锡花岗岩、过铝质含锡花岗岩和过铝质含钨花岗岩）的成矿矿物学特征。以湖南骑田岭花岗岩复式岩体为实例,进行了芙蓉- 菜岭含锡花岗岩和新田岭含钨花岗岩的成矿矿物学对比研究。前者以黑云母、榍石为典型含锡矿物,它们在流体富集阶段,经热液蚀变作用,导致锡的淋滤和结晶富集作用;后者则以出现岩浆白钨矿和黑钨矿为特征。提出的钨锡花岗岩成矿矿物学研究体系有助于深化矿床学研究和矿床勘探工作,并将在今后工作中进一步完善。     

Early Proterozoic syn-and postcollision granites in the northern part of the Baikal fold area

Early Proterozoic granitoids are of a limited occurrence in the Baikal fold area being confined here exclusively to an arcuate belt delineating the outer contour of Baikalides, where rocks of the Early Precambrian basement are exposed. Geochronological and geochemical study of the Kevakta granite massif and Nichatka complex showed that their origin was related with different stages of geological evolution of the Baikal fold area that progressed in diverse geodynamic environments. The Nichatka complex of syncollision granites was emplaced 1908 ± 5 Ma ago, when the Aldan-Olekma microplate collided with the Nechera terrane. Granites of the Kevakta massif (1846 ± 8 Ma) belong to the South Siberian postcollision magmatic belt that developed since ～1.9 Ga during successive accretion of microplates, continental blocks and island arcs to the Siberian craton. In age and other characteristics, these granites sharply differ from granitoids of the Chuya complex they have been formerly attributed to. Accordingly, it is suggested to divide the former association of granitoids into the Chuya complex proper of diorite-granodiorite association ～2.02 Ga old (Neymark et al., 1998) with geochemical characteristics of island-arc granitoids and the Chuya-Kodar complex of postcollision S-type granitoids 1.85 Ga old. The Early Proterozoic evolution of the Baikal fold area and junction zone with Aldan shield lasted about 170 m.y. that is comparable with development periods of analogous structures in other regions of the world.     

南岭成矿带中—晚侏罗世成钨、成锡、成铅锌（铜）花岗岩的差异性研究

【研究目的】南岭地区以发育强烈的中—晚侏罗世岩浆作用与相关金属成矿作用为主要特色,这些金属矿床尤以钨、锡、铅锌铜最具代表性。对这3类成矿花岗岩开展系统的对比研究,深入分析成矿差异原因,对指导区域找矿具有重要意义。【研究方法】本文通过搜集已发表的主量元素、微量元素、年代学、Sr-Nd-Hf同位素和矿物化学数据,并结合项目组长期野外地质调查进展,对3类成矿花岗岩进行了差异性研究。【研究结果】通过对比发现成钨、成锡、成铅锌铜3类花岗岩在时空分布格局、野外地质特征、矿物组成、源区性质、包体成因类型、岩浆分异程度、形成温度和氧逸度等方面具有明显的差异。【结论】笔者认为花岗岩的岩石地球化学成分、源区物质组成、岩浆分异程度以及岩浆演化过程中物化条件(如氧逸度)的综合差异是导致南岭花岗岩形成3类不同金属矿床的主要原因。在此基础上,进一步完善了南岭成矿带成钨、成锡、成铅锌铜花岗岩的综合判别标志,指导区域找矿勘查。     

Geochemistry of lepidolitic granitoids from the Mungutiyn Tsagaan Durulj occurrence (central Mongolia)

We studied the geologic position, geodynamic setting, petrology, and geochemistry of veined lepidolitic granitoids from the Mungutiyn Tsagaan Durulj (MTD) occurrence (central Mongolia), found within the area of Mesozoic intraplate rare-metal magmatism. It has been established that their trace-element enrichment resulted from the intense effect of fluids rich in F, K, Li, Rb, Cs, Sn, Be, and W, which arrived from a deep magma chamber of rare-metal granitic melts, on leucogranites with originally weak rare-metal mineralization. Very high contents of F, rare alkali metals, Sn, Be, and W, characteristic of MTD granitoids, are close only to those in greisens of rare-metal granites and topaz-lepidolite-albitic pegmatites. The difference from the greisens in each case might be due to the features of the original rocks. The difference between the greisenized MTD leucogranites and the topaz-lepidolite-albitic pegmatites is more radical: Along with evident petrographic distinctions, it includes an evolution trend toward the albite norm decrease, not typical of Li–F igneous rocks; rock shearing and gneissosity, which must have contributed to their chemical transformation according to this trend; and stably lower contents of Nb and Ta (trace elements which usually accumulate during crystallization fractionation of F–Li granitic melts and are poorly soluble in magmatic fluids). The greisenized MTD granitoids are not only high-grade rare-metal ores of Li, Rb, F, and Sn but are also regarded as an indicator of a deep concealed pluton of rare-metal granites.     

Phyllosilicate and rutile compositions as indicators of Sn specialization in some southeastern Australian granites

Biotites from unaltered Sn granites in southeastern Australia are highly ferroan, Fe/(Fe+Mg+Mn) >0.75, whereas biotites from barren granites are less Ferich, Fe/(Fe+Mg+Mn)<0.65. Similar distinctions between Sn-specialized and barren granites can be observed in the other phyllosilicates, especially chlorite. Biotites and muscovites from Sn granites have greater Be, Cs, (F), Li, Mo, Rb, Sc, Sn, Tl, (Y) and Zn and lesser Ba abundances than corresponding micas from barren granites in the same district. Alteration of barren granites also results in similar enrichments in micas. Of these elements, Sn and Zn, because of their abundance and retention during degradation of biotite to chlorite, are the best trace element discriminants between barren granites and Sn granites/altered granites, with the Sn content of phyllosilicates being a better indicator than Zn. Rutile inclusions within phyllosilicates from unaltered Sn granites have Nb₂O₅ contents up to 26%. The Ta content tends to increase with Nb content but especially high Ta contents occur in the rutile inclusions of granites that give rise to pegmatitic deposits. The rutile inclusions in Sn granites may also have substantial Sn and W contents. The rutiles of barren granites have low Nb, Ta, Sn and W contents but Sn and W increase with alteration. Together, the ratio Fe/(Fe+Mg+Mn) and Sn contents in phyllosilicates and rutile compositions can be used to identify the Sn mineralization potential of a granite.     

Geochemistry of Early Paleozoic granitoids of the Baikal region and their geodynamic setting exemplified by the Khamar-Daban Ridge and Olkhon Island

Comparative study of geological and isotope-geochemical features of the Early Paleozoic granitoids of the Khamar-Daban Ridge and Olkhon Island located in the Baikal region has revealed their close age and composition. Besides, they were referred to as syncollisional S-type formations derived from gneiss-schistose substratum of metamorphic sequences.Granitoids of the Solzan massif in the Khamar-Daban Ridge, as well as the Sharanur complex on Olkhon Island, occur in the autochthonous and allochthonous facies. They primarily consist of migmatites, plagiogranites, gneiss granites, and K–Na-granites. The magmatic rocks of the Sharanur complex include subalkaline granosyenites and quartz syenites spatially proximal to K–Na-granites. In the north of the island we investigated alkaline syenites which might be related to the Budun massif of basic rocks. On Olkhon Island in the Tashkiney valley, the surveyors recognized the geochemical type of pegmatoid rare-metal granites bearing beryllium mineralization. As was found, they are distinguished from Be-muscovite and spodumene pegmatites of the Khamar-Daban by high Rb, Cs, Sn, Nb, Ta, and W but low Li concentrations, which is probably due to Li-enrichment in the protolith of the Kornilova Formation relative to the Olkhon sequence. This points to the inheritance of the protolith composition at all stages of syncollisional granite formation.The geochemical study has shown similarity of calc-alkaline and subalkaline granitoids of the Khamar-Daban Ridge and Olkhon Island and their affinity in age and average composition of the regional continental crust. In addition, it has revealed the evidence for the existence of the Olkhon–Khamar-Daban block occurring as a single terrane in the Baikal region.     

江苏主要含矿花岗岩体的地球化学特征及找矿方向

分析了江苏省主要含矿花岗岩体的主元素、微量元素含量,所含黑云母的成分以及包裹体的类型等地球化学特征.结果表明它们大多属于岩浆花岗岩,且以I型花岗岩为主.成矿元素Cu、Pb、Zn在I型含矿花岗岩中普遍有一定程度的富集,其中以Cu的富集程度最好;Cr、Co、Ni在此类岩体中含量亦较高.广泛发育多种包裹体,尤其是发育含子矿物多相包裹体是含矿花岗岩体的重要特征.指出应加强在宁镇中段某些I型花岗岩体中寻找Cu多金属矿的工作.     

Phanerozoic tin and tungsten mineralization—Tectonic controls on the distribution of enriched protoliths and heat sources for crustal melting

Phanerozoic primary tin and tungsten deposits and lithium–cesium–tantalum (LCT) type pegmatites define discontinuous belts that reach several thousand kilometers length. Mineralization along these belts is irregularly distributed, diachronous, and occurs in different tectonic settings on both sides of major sutures. Although these deposits formed during late magmatic differentiation processes, magmatism may be related to different geodynamic settings, in particular subduction, continental collision, and anorogenic extension. Here we test the hypothesis that the formation of these belts is explained by a generic process, involving three independent steps as prerequisite for the development of deposits: (i) intense chemical weathering of sedimentary rocks on a stable continent resulting in the enrichment of Sn and W in the protoliths, (ii) sedimentary—followed by tectonic—accumulation of the enriched debris at continent margins, and (iii) heating of the voluminous sedimentary protoliths generating Sn and/or W enriched melts. The Sn and/or W belts reflect the spatial distribution of enriched protoliths, whereas the discontinuous distribution of Sn and W mineralization within the belts reflects both, the locally extreme sedimentary and tectonic accumulation and the distribution of heat sources.

• (i)Intense chemical weathering results in the preferential loss of most feldspar-bound elements (e.g., Na, Ca, Sr, and Pb) and the residual enrichment of elements incorporated in or adsorbed on clay minerals (e.g., Li, K, Rb, Cs, Sn, and W), i.e., produces some of the hallmark geochemical signatures of tin granites that also are obtained by extreme magmatic fractionation of granitic melts. Intense chemical weathering occurs in tectonically stable areas with limited topography and may be particularly pronounced in the interior of large continental masses, such as late Proterozoic Rodinia, late Proterozoic to Cambrian Gondwana, and late Paleozoic to early Mesozoic Pangea.
• (ii)Sedimentary accumulation occurs when these blankets of chemically intensely weathered sediments are redistributed from the continent interior to the margins of the continent. This fluviatile redistribution is typically related to the fragmentation of megacontinents or supercontinents. Tectonic accumulation may occur when passive-margin sedimentary packages later are reworked in an active margin setting.
• (iii)The nature of the heat source controls type of mineralization and its relation to plate boundaries. Internal heating in orogenically thickened crust generates minimum-temperature melts that mobilize elements hosted in feldspar and muscovite and may generate granites and pegmatites with LCT-type signature. The formation of Sn and W mineralization requires higher temperatures to consume biotite. Such temperatures require heat advection from the mantle by (a) mantle-derived melts in subduction setting, (b) emplacement of ultrahigh-temperature metamorphic rocks that had been subducted to mantle depth during continental collision, or (c) mantle-derived melts in extensional settings. The age of mineralization within belt reflects the event of heat input.

The distribution of Sn and W mineralization within belts is the superposition of processes at the passive margin and processes at the active margin. Source enrichment and distribution is related to megacontinents (chemical weathering) and their fragmentation (sedimentary accumulation at the margin of fragments from a megacontinent). Therefore, Sn and W belts generally border to fragments of former megacontinents. Metal mobilization from the source rocks is controlled by the distribution of the heat sources and, thus, by processes at an active margin. The generic model explains both the arrangement of Sn and W mineralization in belts and their distribution with the belts. It allows for recurrent formation of mineralization within a single belt in contrasting tectonic settings and to both sides of major sutures. With source enrichment and source accumulation being necessary requirements of mineralization, the generic model also explains unmineralized gaps within Sn and W belts and why there are unmineralized magmatic belts of comparable setting and with granitic rocks of comparable magmatic development. Areas without voluminous packages of enriched protoliths or without ample heat sources to mobilize the ore elements from the protoliths have a low potential for hosting Sn and W mineralization.     

南岭地区钨锡铌钽花岗岩及其成矿作用

在晚侏罗世时,南岭地区发生了与花岗岩有关的钨锡铌钽大规模成矿作用。依据花岗岩的岩石学、地球化学及其矿化特征,可将南岭地区含钨锡铌钽花岗岩划分为三个主要类型：含钨花岗岩、含锡钨花岗岩和含钽铌花岗岩。含钨花岗岩的地球化学特征可归纳为铝过饱和,低Ba+Sr 和TiO2,轻重稀土比值低,铕亏损强烈,富Y 和Rb,Rb/Sr 比值高,分异强烈。含锡钨花岗岩总体特征表现为TiO2 含量高,准铝质—弱过铝质,轻重稀土比值和CaO/(K2O+Na2O)比值高,富高场强元素、稀土、Ba+Sr 和Rb,低Rb/Sr 比值,分异演化程度较低。含钽铌花岗岩的地球化学特征主要为TiO2 含量和CaO/(K2O+Na2O)比值低,Al2O3/TiO2 和Rb/Sr 比值明显偏高,强过铝质,贫Ba+Sr、稀土和高场强元素,铕亏损强烈,明显富Rb 和Nb,高度分异演化。三类含矿花岗岩具有明显不同的演化特征,成矿作用与它们的演化密切相关。黑云母花岗岩主要与锡成矿作用有关,二云母花岗岩和白云母花岗岩主要产生钨矿化或锡钨共生矿化,钠长石花岗岩主要与钽铌或锡（钨）钽铌矿化有关。总结了南岭锡钨钽铌矿床的重要类型,提出了绿泥石化花岗岩型锡矿新类型,指出南岭地区要特别注意在含锡钨花岗岩中寻找此类锡矿和云英岩- 石英脉型锡钨矿。